1. Technical Field
The present disclosure relates to drop tube segments and, more particularly, to drop tube segments providing selective access to a fluid reservoir.
2. Description of the Related Art
Underground storage tanks are routinely utilized to store fuels such as gasoline, diesel fuel, ethanol, etc. for later dispensing to vehicles through fuel dispensers. The underground storage tank contains an inlet through which fuel is provided to the underground storage tank, typically by a tanker truck. A plurality of fuel dispensers are also fluidly connected to the underground storage tank and are utilized to provide the fuel contained therein to, e.g., passenger vehicles.
Typically, a riser pipe extends upwardly from the underground storage tank to a fill connection point contained within a sump at the fueling station. Within the riser pipe, a drop tube extends downwardly into the volume of the underground storage tank.
The drop tube extends toward the bottom of the underground storage tank so that the outlet end of the drop tube is covered by the motor fuel or other liquid contained in the underground storage tank. Therefore, the drop tube is not in fluid communication with the fuel vapor contained in the ullage area of the underground storage tank. However, the overfill prevention valve is typically positioned much closer to the top of the underground storage tank and is therefore typically in fluid communication with the vapor contained in the ullage area of the underground storage tank.
When filling an underground storage tank, the operator of a tanker truck must be careful not to overfill the underground storage tank. To this end, an overfill prevention valve may be utilized to prevent overfilling of the underground storage tank. For example, an overfill prevention valve may utilize a float which is buoyant on a surface of a quantity of motor fuel and which is connected by a linkage to a valve positioned within a segment of a drop tube connecting a fill point to the underground storage tank. The linkage extends through the wall of the drop tube so that it can mechanically connect the float, which is outside of the drop tube, to the valve body, which is inside the drop tube. When the float rises to a “filled” position as the fuel level approaches the top the tank, the linkage causes the valve to close. When closed, incoming fuel quickly builds up above the valve in the drop tube, causing the operator to stop the flow of fuel.
Because the overfill prevention valves of prior art devices include a mechanical linkage connecting a float positioned on the exterior of the drop tube with a valve body positioned on the interior of the drop tube, the wall of the drop tube segment containing the overfill prevention valve must be physically penetrated by the linkage to allow for such a connection. This physical penetration of the wall of the drop tube segment containing the overfill prevention valve creates a leak point where vapor contained in the ullage space of the underground storage tank can enter into the drop tube. It is desirable to prevent vapor contained in the ullage space of the underground storage tank from entering into the interior of the drop tube where it could potentially be vented to the atmosphere.
In order to verify that the overfill prevention valve is working properly, it may be desirable to include a testing functionality whereby the valve can be actuated selectively, without the need for an actual overfill condition.